Heretofore, in an automated assembly line for automobiles, an assembly process has been performed in which clamping is carried out by a clamp apparatus under a condition in which pre-formed frames are positioned in an overlaid manner and the frames are welded together.
In one such clamp apparatus, as disclosed in Japanese Patent No. 4950123, left and right clamp arms are provided as a pair, the clamp arms being disposed for rotation respectively through pins. Further, proximal ends of the clamp arms are supported pivotally by a base to which a drive unit in the form of an air cylinder is connected, whereby distal ends of the clamp arms are operated to open and close. Thus, a workpiece such as a frame or the like is gripped from the left and right by the distal ends of the pair of clamp arms.